Wireless signaling system.



I. LANGMUIR.

wmusss smmlms svs`fm.

APPLICATON FILED HAIL Il. I9l6.

1,313,093. Patented Aug.'12,1919.

Jill,

Inventor:

Hls .J'ttorneg UNITED STATES PATENT OFFICE.

IBVING LANGMUIR. 0F BCHENEOTADY, NEW YORK, ABSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK..

WIRELESS SIGNALING SYSTEM'.

Specication of Letters Patent.

Patented Ang, 1 .e, 1 g19.

Application tiled Ilm-ch 11, 1918. Serial No. 88,687.

To all 4whom 'it may conce'm Be it known that I, Invnm LANGMUIR, a citizen of the United States, residing at Schenectady, in t'he county of Schenect-ady, State of New York, have invented certain new and useful Improvements in Wirele Signa-ling Systemsv` of which the following is a specification.

My present invention relates to wireless signaling systems` and more particularly to an improvement in the so-called heterodyne system of wireless transmission. In this system it has been customary heretofore to provide at the receiving station a, source of sustained oscillations having a frequency slightly different from that of the waves used for transmitting the signals which it is desired to receive. oscillations from this local source have been caused to interact with the waves received from the distant station and produce, in a suitable device. signals, either visual or audible. In case the si nals are rendered audible they may take t e form of beats having a frequenc)v dependent on the difference in frequency between the received and locally produced oscillations.

Various forms of apparatus for producing audible signals have been suggested. In

a prior application, Serial No. 809,248, filed by me 0n December 29, 1913, I have described a system .in which the received and locally generated oscillations have been caused to interact and produce beats in a telephone receiver through the medium of an electron discharge device. In this case at least two separate agencies are r uired to effect the desired result, namely, a evice for producing hi h frequency osciilations and an electron ischarge device. I have discovered, however, that if an electron discharge device is used as a source of oscillations it may at the same time serve as the agency through which the two sets of oscil lations interact to produce siials.

The novel features which believe to be characteristic of my invention I have pointed out with particularity in the claims appended hereto. The invention itself, however, both as to the details of its organization and its mode of operation will be best understood by reference to the following description taken in connection with the accompanyin g drawing in which I have shown u single system of connections whereby the desired result may be accomplished.

.In the drawin 1 represents an electron discharge tube w lich comprises an evacuated tube 2 having a cathode 3, an anode 4, and a conducting body 5 which is preferably in the form of a grid interposed between the cathode and anode. The cathode used in this case is in the form of a filament which may be raised to incandescence by current from any convenient source, as battery 6. The two electrodes are connected by an oscillatory circuit, containing an external source of current 7, which may be a battery, as shown, or any other direct current source, an inductance 8 and an indicating device which in this case takes the form of a telephone receiver 10. The circuit thus formed for convenience of description I call the plate circuit. The cathode 1s also connected externally with the grid 5 through an inductance 9. The oscillatory circuit thus formed I designate the grid circuit. The two circuits are coupled together by placing the inductance 8 in inductive relation with the inductancc 9. With the circuit arrangement shown, if the inductances 8 and 9 are wound in the same direction, when current in the plate circuit begins to build up current tends to fiow in the opposite direction in the grid circuit and the a id becomes negatively electrified. This cuts down the flow of current in the plate circuit and as the current decreases the grid loses its negative potential and becomes positive. This allows the current to increase again in the plate circuit. These changes may take place with great rapidity, their fre uency depending upon the natural perlods of thetwo circuits. The frequency of the current changes may be readily varied by varying the constants of the two circuits by means of the adjustable condensers 11 and 12 placed respectively in the grid and plate clrcuits. By this means sustained oscillations of any desired frequency may be obtained in the coil 9 and the frequency ma easil be adjusted to a value sllghtly di erent rom that of the waves which it is desired to receive.

Since an alternating current is produced in coil 13 there will in turn be an alternating potential induced in coil 8 in the plate circuit. Hence the total current in the plate circuit will be the resultant of the current flowing therein from the battery and the oscillatory current produced by this induced potential. The latter component may be so small that the total current in the circuit will always be in the same direction though in some cases it ma be so large that there is a reversal in the irection of current flow. In any case, however, the tota-1 current may be considered as being made up of two components one of which is an oscillatory current.

Since in most cases it will be desirable to employ fre uencies beyond the range of audibility oil a telephone receiver, these locally produced current changes will have no effect in the receiver 10. If, however, the coil 9 is connected inductively with coil 13 of the grounded aerial 14, the received oscillations will be impressed upon the grid 5 of the electron discharge tube. These oscillations will produce a rapid variation in the potential of the grid `which in turn will produce correspondin variations in the current flowing throu h t e tube. Inasmuch as the freuency o the received oscillations differs rom the frequency of the current changes set up locally in the plate circuit there will be certain periods when the two sets of oscillations are in phase with each other when they will act together and roduce increased changes in the current dbw through the plate circuit. There will also be periods when they are directly opposite in hase and the current chan es in the plate circuit will be correspondingy reduced. As a result of this action the current flowing through the telephone receiver 10instead of having a constant amplitude will have a regularly varying amplitude. Beats will consequently be heard in the receiver, the freqlliency of these beats bei dependent upon t e group frequenc of t e current variations produced in t e plaie circuit and this roup frequency in turn being equal to the iiierence in frequency of the two sources. With this arrangement Vthe only si als which can be received are those whic are transmitted by means of waves which dilfer in frequency from the locally produced os'- cillations by an amount which 1s within the ran of audibility of an ordina telephone receiver. The waves which di er in frequency from the locally produced waves by a greater or less amount than the audible fre. quency of the receiver will roduce no eect.

It will of course beun erstood that :the current llowing in the plate circuit is made up of a large number of rapidly succeeding unidirectional impulses of brief duration. account of the high frequency of these lmpulses the inductance of the receiver will tend to choke them back. To prevent this the condenser 15 may be shunted across theterminals of the receiver. In some cases it will found desirable to emplo a battery 16 1n the grid circuit in or er that nominally the grid may have a certain definite potential with respect to the cathode. The amount of this tential will depend upon the design of t e tube and upon the desired characteristics of the tube. It may be found advantageous in some cases to make the battery so large that the potential of the grid will always be negative. On the other and it may be found desirable in sorriecases to so connect the battery that a positive potential will be imposed upon the grid. It. will of course be understood that other suitable forms of current operated devices than a telephone receiver may be used for receiving the signals and in case the current fiuctuations produced are not great enough to operate the indicating means, the may be amplified by means of an ampli ying device desired.

ile I have shown and described only a single organization whereby the desired result may be accomplished, it will be apparent that many modifications may be made Awithout departing from the spirit of my invention. I do not wish to be limited to the particular forms of apparatus indicated as other forms may also be used for the saine pur se.

at I claim as new and desire to secure by Letters Patent of the United States, is

1. The combination in a wireless receiving system of an antenna, an electron dischar e device having resonant plate and grid c1rcuits, inductances in each of said circuits which are coupled to each other whereb local oscillations may be roduced of a di ferent frequency from tlibt of the oscillations to be received, and a coil in said antenna which is coupled to both of said inductances.

2. The combination in a wireless receiving system of an antenna, device having resonant plate and -grid circuits, a coupling between said circuits whereby local oscillations may be produced of a different frequency from that of thefoscillations-to be received, and a couplingbetween each of said circuits and the antenna.

In witness whereof, I have hereunto set my hand this 10th d of March 1916.

In NG LANMUiR.

an electron discharge 

